Oxidation of Cu(I) by oxygen in concentrated NaCl solutions—III. Kinetics in a stirred two-phase and three-phase reactor

A whole set of data on the oxidation of cuprous chloride in a standard stirred reactor is treated using the recent work by Papassiopi and co-workers (Chem. Engng Sci.40, 1527 and thesis, Ecole des Mines de Paris) on homogèneous kinetics. The reaction regime is found to be a slow one and HCl and NaCl concentrations, temperature, volume of solution and stirring speed only influence the quantity k_La (mass-transfer coefficient × specific interfacial area) or the oxygen solubility or both. The system Cu(I)/O₂ is then adequate to measure k_La in gas—liquid contactors. The improvement of oxidation when an immiscible organic phase is added may be attributed either to the decrease of the water surface tension or to the formation of “two-phase bubbles“ or “gas—liquid drops”, more unlikely at low stirring speed.     

Performance of an RTL contactor for gas-liquid systems: Effective interfacial area and volumetric mass transfer coefficient by oxidation of sodium sulphite solution

Effective interfacial area a and volumetric liquid-side mass transfer coefficient k_La of an RTL contactor were obtained at different stirring speeds by absorption of oxygen from air into 0.8 kmol/m³ sodium sulphite solution, in the presence of Co⁺⁺ ions. The values of a and k_La ranged from 80 to 150 m²/m³ and 0.0003 to 0.00053 s^?1, respectively, when stirrer speed was increased from 8 to 40 rpm. When k_L alone was evaluated, it was found to be practically constant, irrespective of stirring speed.     

A study of oxygen absorption kinetics in ionic Cu(I) aqueous solutions

We developed the oxidation reaction of Cu(I) ion in aqueous hydrochloric solution by oxygen in a gas-lift capillary bubble column. The method of gas-liquid absorption with chemical reaction was used. Test data confirmed that the rate constant of the reaction is strongly affected by solution compositions, and that chloride ions induce an inhibition effect. The kinetical orders found are equal to 1 and 2 for oxygen and Cu(I) respectively. The influence of temperature on reaction rate constant showed the existence of a maximum value between 303 and 313K. The effect of gas-liquid of gas-liquid system on the liquid-side mass transfer coefficient k_L was also investigated.     

The electrochemical oxidation of alkaline copper cyanide solutions

A systematic investigation of the electrochemical oxidation of copper cyanide was carried out. At low pH, cyanide destruction is believed to be catalyzed by the heterogeneous reaction involving adsorbed [Cu(CN)₃]²⁻ and possibly [Cu(CN)₄]³⁻. At high pH, rapid oxidation of cyanide was observed around 0.75 V versus Hg/HgO with the formation of a black copper oxide film. This enhanced electrocatalytic activity is believed to be related to the formation of an active copper(III) species. The transition point between low and high pH as a function of cyanide and copper concentrations is discussed. Bulk electrolysis of a copper cyanide solution at 0.90 V oxidized most of the cyanide to cyanate. Prolonged electrolysis further oxidized the cyanate to nitrate. The copper oxide film is found to be catalytic, capable of electro-oxidizing hydroxide to oxygen and cyanate to nitrate.     

The oxidation of aqueous sodium sulphite solutions

In this paper new experimental work on the kinetics of the absorption of oxygen in an aqueous solution of sodium sulphite with cobaltous sulphate as a catalyst, has been presented and compared with already published data. It is shown that the reaction of oxygen with sodium sulphite is zero order in sulphite, first order in cobalt and second order in oxygen for 2 × 10⁴ N/m² <p_O2 < 10⁵ N/m², 150°C <T < 60°C, 3 × 10^?6 kmol/m³ <c_Co⁺⁺ < 3 × 10^?3 kmol/m 7.50 < pH < 8.50 and 0.4 kmol/m² <c_SO2-- < 0.8 kmol/m³. The reaction rate constant can be varied by more than two decades by changing the cobalt concentration, pH and temperature.The specific interfacial areas, a, and mass transfer coefficients, k_L, measured by DeWaal and Beek [14, 15] using an incorrect kinetic model of this reaction, are reinterpreted with the results of the present kinetic investigation. It is shown that their values of a and k_L are a factor 2.2 too low and too high, respectively, but that their values of k_La are correct.     

Isomerization of α-pinene to camphene

The catalytic isomerization reaction of α-pinene to camphene over a clinoptilolite catalyst was investigated in a batch reactor open to the atmosphere between 130 and 155°C. The catalyst was selective to the isomerization of α-pinene to camphene. The effects of several variables, such as reaction temperature, amount of catalyst, stirring speed and catalyst particle size, on the conversion of α-pinene and selectivity to camphene were determined. The reaction fits a first-order parallel reaction with rate constants of k ₁ = 3.020·10^?2 e ^?33381.6/RT for the production of camphene and of k ₂ = 1.576·10^?2 e ^?31096.53/RT for the production of limonene.     

A contribution to the measurement of oxygen mass transfer in a laboratory pressure reactor

A method was used to measure the liquid‐side volumetric coefficient of oxygen mass transfer (k_La) in closed, semi‐batch pressure reactors used in hydrometallurgical laboratories. In this method, the oxygen pressure was monitored as oxygen was continuously sparged into a pressure vessel containing a sodium sulfite solution. A material balance equation was derived for oxygen in the vessel and the experimental data were fitted to this equation. From the constant parameters of the equation, k_La was calculated. The solution in the vessel also contained an appropriate amount of cobalt catalyst so that oxygen was consumed rapidly by oxidation of sulfite to sulfate. Under these conditions, the oxygen concentration in the bulk liquid phase could be assumed to be equal to zero. Values of k_La determined by the method under various conditions were reproduced within 12% deviation from the average values. k_La was found to increase moderately with temperature in the range of 25 to 75 °C, with an activation energy of 33.09 ± 1.33 kJ mol⁻¹. The presence of hydrophobic or hydrophilic solids was found to have a deleterious effect on k_La. © 2000 Society of Chemical Industry     

OXIDATION OF GLUCOSE ON SUSPENDED PT/C: REACTION KINETICS AND ABSORPTION STUDIES

In search of a suitable model reaction system for studying hydrodynamic properties of slurry reactors under reactive conditions, the oxidation of glucose on a suspended Pt/C catalyst was investigated. In addition to homogeneous kinetic measurements, gas absorption experiments in a stirred cell with a plane interface were also carried out at 25 to 45^°C using finely powdered catalyst particles. It was found that the oxygen consumption rale followed first order kinetics only at the very beginning of the reaction. If the total amount of reacted oxygen was considerably more than that of the initial saturation value (i.e. kinetic runs repeated after some time of aeration under vigorous stirring or lengthy gas absorption experiments), the order with respect to oxygen was ½ Furthermore, the half order rate constant dropped to about ½ to ¼ of its initial value and was constant only after an amount of about 1.5 x 10^?2mol O₂/g catalyst was reacted. A new plot is also proposed which permits the simultaneous determination of the volumetric mass transfer coefficients and the rate constants for a half order reaction from gas absorption experiments at various catalyst concentrations. The rate constants and the k_La values which were obtained from completely different methods were in reasonable agreement.     

Liquid-solid mass transfer in a rotating packed bed reactor with structured foam packing

A rotating packed bed (RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient (k_LS) have been investigated. The correlation for predicting k_LS was proposed, and the deviation between the experimental and predicted values was within ± 12%. The liquid–solid volumetric mass transfer coefficient (k_LSa_LS) ranged from 0.04–0.14 1⁻¹, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.     

Scale Effects on Hydrodynamic and Mass Transfer Characteristics of External Loop Airlift Reactors

Gas hold-up and oxygen transfer have been investigated in two geometrically similar external loop airlift reactors of linear scale ratio of 2. In mass transfer experiments, the sampling location was found to be important as significantly different k_La values can be obtained. The variations of k_La with probe location have been explained in terms of non-uniform hydrodynamic properties and the results obtained have been validated by means of high speed video camera recordings. At higher gas flowrates, the gas hold-up was significantly higher in the large-scale reactor. It was found that in order to maintain the gas hold-up or k_La constant in both the small- and large-scale reactor, the small-scale reactor required 25% and 27% more power input per unit volume of liquid respectively. © 1997 SCI.     

Mass transfer characteristics of a novel gas-evolving electrochemical reactor

Mass transfer coefficients were measured for the deposition of copper from acidified copper sulphate solution at a vertical-plate cathode stirred by the oxygen evolved at a coplanar, vertical-plate lead anode placed upstream from the cathode. The variables studied were: oxygen discharge rate, electrolyte concentration and height of the cathode. The cathodic mass transfer coefficient was increased by a factor of the order of 2 to 5 over the natural convection value depending on the rate of oxygen discharge at the lead anode. The relationship between the mass transfer coefficient and the oxygen discharge rate was found to be logK=a+0.296 logV.The mass transfer coefficient was found to decrease initially with increasing electrode height, but then reached a constant value independent of further change in electrode height. A new, modified parallelplate reactor stirred by the counter electrode gases is described. The advantage of the design is that it offers more efficient stirring with no added power consumption. Details of the design are discussed.Nomenclature C concentration of CuS0₄ (mol cm^–3) - F Faraday's constant - h electrode height (cm) - K mass transfer coefficient (cm s^–1) - l _L limiting current density (A cm^–2) - V gas discharge rate (cm s^–1) - z number of electrons involved in the reaction On leave from the Department of Chemical Engineering, Faculty of Engineering, Alexandria University, Alexandria Egypt.     

PRECIPITATION CONDITIONS OF CHEVREUL'S SALT FROM SYNTHETIC AQUEOUS CuSO4 SOLUTIONS

In this study, synthetic aqueous CuSO₄ solution was prepared at various concentrations. Chevreul's salt was precipitated by passing SO₂ through these solutions. Chevreul's salt, a mixed valence copper sulfite, Cu₂SO₃·CuSO₃·2H₂O, was characterized by XRD and SEM. The effects of parameters such as initial solution concentration, SO₂ feeding rate, reaction time, and initial solution pH on precipitation of Chevreul's salt were investigated. 2ⁿ factorial experimental design and orthogonal central composite design methods in the precipitation experiments were used. It was observed that the effective parameters on the precipitation of Chevreul's salt were initial solution concentration, SO₂ feeding rate, and initial solution pH. The optimum conditions obtained for maximum copper precipitation were: initial solution concentration 1.14 M, SO₂ feeding rate 329.35 L.h.^?1, reaction time 25 min, and initial solution pH 8.5. Constant parameters chosen at the initial stage of the reaction were: temperature 62°C, stirring speed 600 rpm, and reaction pH 3 (Çalban et al., 2006). Under these optimum conditions, the percentage of precipitated copper from synthetic aqueous CuSO₄ solutions was 99.95.     

Effect of fluid rheological properties on mass transfer in a bioreactor

Rheological properties and oxygen mass transfer coefficient (k_L a) were investigated in a stirred reactor (10 dm³) in the course of fermentations producing microbial polysaccharides—pullulan and xanthan. The fermentation broths behaved as pseudoplastic non-Newtonian fluids in both cases. Studies on the relationship between fluid rheological properties and k_L a were also carried out. The oxygen mass transfer coefficient decreases during the fermentation and exponential equations have been obtained to describe the relationship between the oxygen mass transfer coefficient, the agitation speed and the apparent viscosity of the broths. Furthermore, comparison of results between pullulan and xanthan fermentations was investigated. For the xanthan fermentation process, mixing and mass transfer in the reactor were more difficult than those for the pullulan fermentation.     

Influence of temperature and pH on the kinetics of the Sharon nitritation process

The SHARON (Single reactor High activity Ammonia Removal Over Nitrite) process is an innovative process that improves the sustainability of wastewater treatment, especially when combined with an Anammox process. It aims at ammonium oxidation to nitrite only, while preventing further nitrate formation. In order to optimize this process by means of modelling and simulation, parameters of the biological processes have to be assessed. Batch tests with SHARON sludge clearly showed that ammonia rather than ammonium is the actual substrate and nitrous acid rather than nitrite is the actual inhibitor of the ammonium oxidation in the SHARON process. From these batch tests the ammonia affinity constant, the nitrous acid inhibition constant and the oxygen affinity constant were determined to be 0.75 mgNH₃‐N L^?1, 2.04 mgHNO₂‐N L^?1 and 0.94 mgO₂ L^?1. The influence of pH and temperature on the oxygen uptake rate of SHARON biomass was determined, indicating the existence of a pH interval between 6.5 and 8 and a temperature interval from 35 to 45 °C where the biomass activity is maximal. The kinetic parameters of the SHARON process were determined based on batch experiments. These parameters can now be implemented in a simulation model for further optimization of the SHARON process. Copyright © 2007 Society of Chemical Industry     

Copper-poly(2-aminodiphenylamine) as a novel and low cost electrocatalyst for electrocatalytic oxidation of methanol in alkaline solution

In the present work we demonstrate the carbon paste as a new electrode substrate for the electropolymerization of 2-aminodiphenylamine and fabrication of polymer film modified electrode. Then transition metal of copper is incorporated into the polymer by electrodepositing of Cu(II) from CuCl₂ acidic solution using potentiostatic technique. The electrocatalytic oxidation of methanol was studies by cyclic voltammetry and chronoamperometry methods at the surface of obtained Cu/P(2ADPA)/MCPE. It has been found that in the course of an anodic potential sweep, the electro-oxidation of methanol follows the formation of Cu(III) and is catalyzed by this species through a mediated electron transfer mechanism. The obtained current density for this catalytic oxidation is very high which could be come from high surface area of caused by the P(2ADPA) modification. The effects of various parameters such as the copper loading, scan rate and methanol concentration on the electrocatalytic oxidation of methanol were also investigated at the surface of Cu/P(2ADPA)/MCPE. Finally, using a chronoamperometric method, the catalytic rate constant (k) for methanol was found to be 0.2 × 10⁵ cm³ mol⁻¹ s⁻¹ that the high k can be ascribed for the fast electron transfer process due to electrode modification.     

Thermal decomposition studies on copper-chromium-silver impregnated activated charcoal

Thermal gravimetric analyses (TGA) were used to examine the thermal decomposition kinetics of ASC whetlerite, a copper-chromium-silver impregnated activated charcoal. In the low temperature region (< 490 K) the proposed decomposition reaction involves the reduction of the copper chromate species into a copper chromite form accompanied by the oxidation of the carbon support to carbon dioxide. The first order decomposition rate constant was determined to be k_l = 1.22 × 10³exp(− 4.4 × 10⁴/RT). In the high temperature region (598 K to 678 K) a supported cupric oxide species is proposed to react with the carbon support resulting in the formation of cuprous oxide and carbon dioxide. The first order decomposition rate constant for this reaction was evaluated to be k_h = 6.92 × 10⁻²exp(−3.7 × 10⁴/RT).     

A three‐phase fluidized bed reactor in the combined anaerobic/aerobic treatment of wastewater

Aerobic degradation or polishing is an essential step in the combined anaerobic/aerobic treatment of wastewater. In this study, a type of porous glass beads was used for immobilization of microbial cells in a three‐phase aerobic fluidized bed reactor (AFBR) with an external liquid circulation. The effects of superficial gas and liquid velocities on bed expansion, solid and gas hold‐ups and specific oxygen mass transfer rate, k_La, were investigated. A tracer study showed that the mixing and flow pattern in the 8 dm³ reactor could be simulated by a non‐ideal model of two continuous stirred tank reactors (CSTRs) in series. By treating an effluent from an upflow anaerobic sludge blanket (UASB) digester, the distribution of suspended and immobilized biomass in the reactor as well as the kinetics of COD removal were determined. The specific oxygen mass transfer rate, k_La, at a superficial gas velocity of 0.7 cm s⁻¹ dropped by about 30% from 32 h⁻¹ in tap water to 22 h⁻¹ after a carrier load of 15% (v/v) was added. The measured k_La further dropped by about 20% to 18 h⁻¹ in the wastewater, a typical value of the bubbling fermenters with no stirring. Compared with the aerobic heterotrophs under optimum growth conditions, the microbes in this reactor which was fed with anaerobic effluent plus biomass behaved like oligotrophs and showed slow specific COD removal rates. This might be attributed to the presence of a significant amount of obligate anaerobes and facultative organisms in the aerobic reactor. This was confirmed by a relatively low intrinsic oxygen uptake rate of the microbial population in the reactor, 94 mg O₂ dm⁻³ h⁻¹ or 19 mg O₂g VS⁻¹ h⁻¹. © 1999 Society of Chemical Industry     

An empirical model for kinetics of boron removal from boron-containing wastewaters by ion exchange in a batch reactor

In this study, it was investigated boron removal from boron containing wastewaters prepared synthetically. The experiments in which Amberlite IRA 743, boron specific resin was used was carried out in a batch reactor. The ratio of resin/boron solution, boron concentration, stirring speed and temperature were selected as experimental parameters. The obtained experimental results showed that percent of boron removal increased with increasing ratio of resin/boron solution and with decreasing boron concentration in the solution. Stirring speed and temperature had not significant effects on the percent of total boron removal, but they increased the starting boron removal rate. As a result, it was seen that about 99 % of boron in the wastewater could be removed at optimum conditions. On the other hand, the process kinetics were predicted by using heterogeneous fluid-solid reaction models. It was seen statistically that the kinetics of this process agreed the pseudo- second order model, as follows: X_Bl(1−X_B) = 11,241.5[OH][C]^−1.76[S/L]^2.17exp(−19,57l.2/RT)t^1.24     

One-pot template synthesis and crystal structure of two new polyaza copper(II) complexes

A new 14-membered hexazamacrocyclic copper(II) complex [Cu(H₂L¹)](ClO₄)₄(L¹=1,8-bis(2-aminoethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been prepared by the one-pot reaction of ethylenediamine and formaldehyde in the presence of the Cu(II) ion. The crystal structure of [Cu(H₂L¹)](ClO₄)₄ was determined by X-ray diffraction. It crystallizes in the triclinic space group P−1 with a=12.118(2) Å, b=12.438(2) Å, c=12.466(2) Å, α=102.26(1)°, β=112.82(1)°, γ=111.51(1)°, and Z=2. The coordination geometry around the copper(II) ions is axially elongated octahedral with four nitrogen atoms of the macrocycle [Cu–N 2.012(7) Å for Cu(1) and 2.013(6) Å for Cu(2), average value] and two oxygen atoms of two ClO₄⁻ anions [Cu–O=2.550 Å for Cu(1) and 2.601(6) Å for Cu(2)]. [CuL²](ClO₄)₂(L²=3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo[3,3,2]decane) with a novel tetraazabicyclic ligand was obtained from the same reaction system as an additional product. Crystal structure of [CuL²](ClO₄)₂: monoclinic space group Cc, a=16.393(3) Å, b=8.8640(18) Å, c= 13.085(3) Å, β=105.01(3)°, and Z=4.     

Oxidation of Cu(II)-EDTA in supercritical water—Experimental results and modeling

Copper complex ethylenediamine tetraacetic acid (Cu(II)-EDTA) was oxidized in supercritical water in a continuous tubular reactor at temperatures 420–500 °C, residence times 57–144 s, and a pressure 25 MPa. The major carbon-containing products were CO₂ and CO. The TOC conversions increased steadily with reaction temperature and residence time, and the yield of CO can be effectively reduced at elevating temperatures. Ammonia was determined to be the main refractory nitrogen-containing intermediate, whose oxidation was supposed to be enhanced by the copper in Cu(II)-EDTA. In addition, the copper transformed into copper oxides (CuO and Cu₂O), and was removed from the Cu(II)-EDTA solution with high efficiency. Based on the experimental results and the analysis of reaction pathways, a global Arrhenius kinetic model was proposed to predict the removal of TOC and the yield of the intermediates NH₃ and CO. With this kinetic model, a computational fluid dynamic (CFD) model of the tubular reactor was implemented to assist the experimental study. The composition profiles of TOC, CO, and CO₂ along the reactor were simulated and compared with the experimental results. Operating parameters, reaction temperature and oxygen flow rate, were optimized based on the simulation results.